1. Field of the Invention
Cholesteric liquid crystals exhibit brilliant iridescent colors when exposed to various environmental changes such as temperature, pressure, electric fields or contaminants. The response of the liquid crystals can be varied in a variety of ways, including the addition of other materials.
The cholesteric liquid crystals are, for the most part, greasy, buttery substances, which remain soft and difficult to handle and coat. Their use is therefore severely limited, unless means are provided to enhance the ease of handling. Several methods have been developed, which either encapsulate or emulsify the liquid crystals, into a system which is convenient to handle.
The encapsulation technique coats small droplets of liquid crystals with a protective shell, particularly with water soluble polymeric materials. The coating, while protecting the liquid crystals, and enhancing the ease of handling, severely reduces the intensity of the color. The texture and thickness requirements of the encapsulated materials makes mass production difficult, and the encapsulated liquid particles cannot be readily silk screened or printed.
By strongly agitating liquid crystals in a latex, the liquid crystals can be dispersed as small droplets. The percentage of liquid crystals which are capable of handling in this manner is small, and the color of the finished film poor. Furthermore, the emulsion would tend to break down in time, with the liquid crystals floating to the surface.
The various colors which the cholesteric materials undergo in their temperature responsive range are naturally brilliant. However, when the cholesteric materials are combined with other materials or are coated, the colors can undergo substantial dulling. Therefore, it is important when combining the liquid crystal compositions with other materials which serve to fix the liquid crystals to a surface and provide protection for the liquid crystals, that the medium be relatively inert and be clear, as well as capable of bonding to additional films or coatings.
2. Description of the Prior Art
U.S. Pat. Nos. 3,697,297 and 3,732,119 disclose methods of encapsulation of liquid crystals. U.S. Pat. No. 3,600,060 uses water soluble film forming polymers and emulsifies liquid crystals in an aqueous medium. U.S. Pat. No. 3,620,889 incorporates liquid crystals in a clear plastic resin from a solution of the resin in an aromatic hydrocarbon solvent. U.S. Pat. Nos. 3,655,971; 3,663,390 and 3,666,948 use various forms of electromagnetic radiation to form images on films of liquid crystal compositions.